I'm wondering if you guys are aware of any simple C# projects that I can contribute to.Small open source projects tend to be very personal, like one or two dudes team. You'll have a hard time convincing them they need your contributions.
You could fork something and expand it instead, but without a use case its useless (developing libraries in the void tends to do that).
So I don't think this is a feasible approach.
What you could do is develop your own projects, but read about the libraries you use, see their sources, see how they're developed. Maybe then, after you've used them, understood their development and gained experience, you can start to contribute back.
And as always, bug reports, those are contributions too.